The present invention relates generally to derivatized mass spectrometry sample presentation apparatuses, and more specifically, to mass spectrometry sample presentation apparatuses derivatized with complexes including at least one molecule which modifies a biomolecule.
Conventionally, mass spectrometry is a technique used to characterize analytes by determining their molecular weights. Ordinarily, mass spectrometry involves the steps of: coating a sample presentation apparatus with an analyte, introducing the sample presentation apparatus into the mass spectrometer, volatilizing and ionizing the analyte, accelerating the ionized analyte toward a detector by exposing the ions to an electric and/or a magentic field, and analyzing the data to determine the mass to charge ratio of specific analyte ions.
If an analyte remains intact throughout this process, data will be obtained which corresponds to a molecular weight for the entire intact analyte ion. Typically however, it is beneficial to additionally obtain data corresponding to the molecular weight of various fragments of the analyte. It is also beneficial to obtain data which only corresponds to the pure analyte, even when impurities are present. Therefore, it is advantageous to be able to modify analytes by purifying and/or cleaving them, prior to determining their molecular weight.
In conventional mass spectrometry, the analyte is either modified before it is coated on the sample presentation apparatus, or during the volatilization and ionization steps, which occur inside the mass spectrometer. It is known that biomolecules (e.g. polypeptides, deoxyribonucleic acid (DNA), ribonucleic acid (RNA), or carbohydrates) can be selectively digested at specific locations by exposing them to immobilized complexes. However, it is disadvantageous to modify an analyte before it is coated on the sample presentation apparatus, as this extra step slows the overall process, involves loss of the analyte, and can possibly introduce contaminants. Moreover, if the fragments are generated in solution in a reaction between the analyte and a reagent, the kinetics of the reaction may be rather slow, thus adding further delay. It is also disadvantageous to generate fragments during the volatilization and ionization steps as such methods typically provide little control over the analyte cleavage site and may lead to excessive degradation of the analyte.
It is further known to use the Matrix-Assisted Laser Desorption/Ionization ("MALDI") technique to volatilize and ionize biomolecules in a mass spectrometer. This technique involves surrounding a biomolecule in a special matrix material. A LASER beam, tuned to a frequency where the matrix absorbs, is targeted on the matrix material. The LASER transfers sufficient energy to volatilize a small portion of the matrix material. A small number of analyte molecules are thus carried along with the matrix material into the vapor phase in the mass spectrometer.
Prior to the development of MALDI, analysis of biomolecules by mass spectrometry was quite difficult, if not impossible, since no techniques were available which were gentle enough to volatilize intact biomolecules without any degradation or fragmentation. While the MALDI technique provides an advantageous technique for volatilizing biomolecules, this technique does not provide for generation of analyte fragments or purification of an analyte prior to introducing the analyte onto a sample presentation apparatus. In particular, the need for extra fragmentation or purification steps slow the overall process, wastes valuable analyte, and can introduce contaminants.
It is known from PCT Publication No. 94/28418 to use a sample presentation apparatus for laser desorption and ionization mass spectrometry, wherein the sample presentation apparatus is derivatized with surface associated molecules for promoting desorption and ionization of biomolecules. In such surface-bound biomolecule methods, the surface associated molecules bind biomolecules, and later promote desorption of the biomolecules when they are exposed to LASER radiation. Biomolecule fragments are generated by exposing the surface-bound biomolecules to reagents in solution, and later washing away the reagent. This procedure is problematic because it can introduce contaminants, which reduces the quality of the collected data. Specifically, if any reagent is left on the surface after the washing procedure, it will be the first material to be volatilized by the LASER beam, and may very well swamp the signals from the material of interest, thereby adversely affecting the data.
Moreover, such a process is difficult because it relies on new and unproven systems for volatilizing biomolecules. In contrast, MALDI matrix systems are well studied, and known to effectively and gently volatilize biomolecules. MALDI matrices cannot be used with the surface-associated molecule method because the matrix covers the surface-bound biomolecules, and thus would completely prevent the acquisition of useful data.
Furthermore, it is also disadvantageous to directly bind biomolecules to a sample presentation surface, because this would eliminate the possibility of transferring a modified biomolecule to a second region on the presentation surface or a second presentation surface, where it could be exposed to other modifying reagents. Therefore, any chemical reactions according to the surface-bound analyte method, must be performed sequentially, rather than in parallel. In such sequential methods, the bound analyte must be reacted with one reagent, introduced into the mass spectrometer, removed, and then subsequently reacted with a second reagent. Each of these steps is disadvantageous as it presents an opportunity for contaminating the sample and introduces further delay.
For the foregoing reasons, there is a need for a mass spectrometry sample presentation apparatus which provides a rapid, efficient method for analyzing biomolecules using proven, advantageous MALDI matrices.